The human body includes various lumens, such as blood vessels or other passageways. A lumen may sometimes become at least partially blocked or weakened. For example, a lumen may be at least partially blocked by a tumor, by plaque, or both. An at least partially blocked lumen may be reopened or reinforced with an implantable stent.
A stent is typically a tubular body that is placed in a lumen in the body. A stent may be delivered inside the body by a catheter that supports the stent in a reduced-size configuration as the stent is delivered to a desired deployment site within the body. At the deployment site, the stent may be expanded so that, for example, the stent contacts the walls of the lumen to expand the lumen.
Advancement of the stent through the body may be monitored during deployment. After the stent is delivered to the target site, the stent can be monitored to determine whether the placement thereof is correct and/or the stent is functioning properly. Methods of tracking and monitoring stent after delivery include X-ray fluoroscopy and magnetic resonance imaging (“MRI”).
Some stents or portions thereof are formed of materials exhibiting super-elastic characteristics (e.g., nickel-titanium), which can be particularly beneficial in expanding the stent. One distinct disadvantage of some such stent materials though, is their relatively limited radiopacity. An intracorporeal device, such as a stent, and its delivery system should be radiopaque or fluoroscopically visible to allow the practitioner to visualize position and orientation of the device and delivery system in real time. This is important in tracking delivery of the device and delivery system through the patient's vasculature to the precise desired location. The degree of radiopacity and fluoroscopic visibility depends on the device being more absorptive of x-rays than the surrounding tissue. A greater difference in x-ray absorption thus provides better contrast between the device and the surrounding tissue, and thus better resolution and information as to position and orientation of the device as it is delivered.
Many super-elastic alloy materials, such as nickel-titanium, as well as many other materials employed in stent manufacture, for example, stainless steel and even some cobalt-chromium alloys exhibit less radiopacity than would be desirable.
Radiopacity may be improved by increasing stent wall thickness (e.g., strut thickness) although this detrimentally affects the flexibility of the stent, which flexibility is needed for ease of delivery. In addition, increasing the stent wall thickness may not be acceptable from a practical perspective, as there may simply not be additional space available where the stent is to be delivered within the intended vasculature. One method for increasing fluoroscopic visibility and radiopacity of such stents is to attach one or more radiopaque markers to the stent and/or delivery system.
Despite a number of different approaches for increasing radiopacity, manufacturers and users of stents continue to seek improved stent designs and processing techniques.